Answer:
The correct answer is option A.
Explanation:
Diseconomies of scale refers to the situation when the average cost of production increases with the scale of production.
In a constant perfectly competitive market that is operating at long run equilibrium, the price is $60. Each firm is producing 400 units of output.
Since the firms are in long run equilibrium, the price will be equal to the average total cost.
Now, with an increase in the demand for the product the price increases to $64.
The individual demand curve of the firms will move upwards. This will cause the average total cost to increase as well. The new ATC will be $64.
This happens because of diseconomies of scale involved in the increasing the volume if output after a certain point.